The present invention relates to a keyboard of a type including a plurality of key elements.
German pat. publication no. DE 199 46 471 A1 describes a keyboard of this type in which each key element includes two separate break contacts which are mechanically decoupled and commonly activated, when the key element is actuated. One of the break contacts is of mechanical construction whereas the other break contact is of electronic construction. Each key element has 2*2, i.e. four contact terminals, as output for both break contacts. Thus, n key elements require 4*n contact terminals, when the key elements are connected together to form the keyboard. An exemplified key element of this type is also shown in FIG. 1. Dash-dotted line SE1 denotes a switching element of a safety-oriented key element, including two break contacts O11 and O12 which are opened together, when the key element (not shown) is actuated, so that signals can be tapped on contact terminals K11 and K12 of the break contact O11, and contact terminals K21 and K22 signal that the break contact O12 is activated.
Even when reducing the output per key element to three contact terminals by realizing a common base contact, the keyboard still requires 3*n contact terminals per key element. An exemplified key element of this type is shown in FIG. 2 and includes a switching element SE2 with break contacts O21 and O22, whereby two base contact terminals are united to a single contact terminal K3, while the other two contact terminals of the break contacts O21, O22 are separated from one another and designated by reference numerals K4 and K5.
To date, when the key elements are linked together to form a keyboard, typically all contact terminals are connected individually to energy supply units and evaluation units. As a result, the number of external connections is considerable.
It would therefore be desirable and advantageous to provide an improved keyboard to obviate prior art shortcomings and to minimize the number of external wiring lines.